^{A couple of guys who do this have provided more details in the comments.  Interesting.}

Pipe lining is the process of lining old dirty pipes with a liner that is soaked in a combination of resin and epoxy. Making the old pipes complete new without ripping them out.

https://old.reddit.com/r/Damnthatsinteresting/comments/pal40b/pipe_lining_is_the_process_of_lining_old_dirty/

I'm kind of surprised this wasn't thought of before.  The tech to do this isn't really new, it seems it is just a new way to use older tech to make a job a hell of a lot easier and cheaper.

I don't think it's new. People in the comments mention installations that have been up and running for 40 years.